It is known to use hydrolysed yeast extracts as flavouring materials. Yeast is non-toxic to humans and is normally cultured at high density (high dry cell weight per litre).
The nucleic acid content of filamentous fungi may be reduced by contacting them with water at high temperatures and separating them from the water, and such a process is described for Fusarium in PCT patent Application WO95/23843. We have discovered that the water from which the fungus is separated contains materials which can be used as or converted to flavouring materials for foods, especially if the fungus is Fusarium, for example Fusarium IMI 145,425.
The current invention comprises a method whereby the soluble components lost from filamentous fungal cells as a result of this heat treatment can be isolated and used as, or converted into, flavouring substances for foods.
This invention comprises a method of processing a filamentous fungus to improve its suitability as food which comprises subjecting it in the presence of water to a temperature sufficient to reduce its nucleic acid content substantially characterised by using materials removed from the fungus in the said method directly or after chemical reaction to flavour food.
The invention also comprises a flavouring material for food which is an aqueous solution which comprises nucleic acids removed from a filamentous fungus by contacting it with water at an elevated temperature in which the concentration of dissolved solids is sufficiently high to render the material stable to storage at a temperature of 20xc2x0 C. for a period of one month or is a solid comprising such nucleic acids or is a flavouring material comprising a reaction product of such nucleic acids with a sulphur containing amino acid, hydrogen sulphide or ammonium sulphide.
The flavouring materials when in the form of an aqueous solution preferably comprises at least 30% by weight and more preferably 45 to 60% by weight of solids.
Whilst taste is an important factor in food flavours, the odours of flavouring materials are also important
The soluble components are preferably concentrated from the aqueous solution arising from the nucleic acid reduction step by removing water for example by evaporation, distillation (preferably at reduced pressure) reverse osmosis, freeze drying or freezing out the water as ice leaving an aqueous concentrate. It may suitably be removed by evaporation at reduced pressure for example at a temperature of 40 to 70xc2x0 C.
The dissolved solids may be separated as such or left as a concentrated solution where the Aw (water activity) is reduced sufficiently to ensure biostasis at a range of storage temperatures.
If the nucleic acid content of the filamentous fungus is reduced by raising the temperature of its growth medium the water recovered will contain salts and other nutrients, for example glucose and/or complex nitrogen nutrients in addition to the nucleic acids and other materials derived from the fungus. If the flavour imparted by such materials is required they may be left in the materials, but if not they may either be removed, for example by osmosis or ultrafiltration, or the fungus may be washed before its nucleic acid content is reduced thereby avoiding their presence. In WO95/23843 the removal of nucleic acid from a filamentous fungus in its growing state is described; such a process is an improvement over the treatment of fungus in its resting state, for example in pure water. We have found however that the organism takes a short time to adjust from its growing to its resting state and that providing the nucleic acids are removed soon after it is separated from its growth medium the nucleic acids may be satisfactorily removed according to the procedure of WO95/23843.
We have found that after partial or complete removal of water as aforesaid the concentrate can be used as an alternative to hydrolysed vegetable proteins, yeast autolysates or yeast extract as an additive for food. The materials removed from the fungus of value in the production of savoury flavouring preparations and process flavourings. Because of the savoury nature of the flavour it may be used directly in the flavouring of Snacks, Biscuits, Stocks, Soups, Stews, Sauces and Gravies at inclusion levels of preferably between 0.1 and 15 for example 1 to 10 dry weight %.
We have also found that on heating it produces an attractive roast-type aroma. If desired it may be partially hydrolysed before heating, for example by hydrolysis with acetic acid, to produce modified roast flavours.
It may also be reacted, optionally after at least partial hydrolysis, with sulphur containing amino acids, preferably cysteine or optionally with H2S and/or (NH4)2S to produce savoury flavours.
The savoury nature of the material may be altered by chemical reaction to provide a different flavour profile in that the meaty/roasted flavour notes are increased. Such xe2x80x9creaction flavouringsxe2x80x9d may be used in flavouring Meat (beef, chicken, iamb, pork, etc), meat alternatives (e.g. based on soy, wheat, pea protein, myco-protein), prepared meals, snacks and drinks at incusion levels of preferably between 0.1 and 10 for example 1 to 8 dry weight %.
The flavourings may be produced by reacting materials removed from the fungus as aforesaid with cysteine. This may be carried out in the presence of water if desired; for example a 1.5 to 75 and preferably a 5 to 50 weight % solution of such materials may be reacted with cysteine in quantities of up to 10%, for example 1 to 5% of cysteine by weight based on such materials. The reaction may be carried out at a temperature of for example 110 to 140xc2x0 C. at a pH of 5.5 to 9. Reaction is suitably continued for 0.5 to 7.5 hours.
It is believed that hydrolysis increases the free ribose content of the concentrate and this may be appropriate if certain flavours are desired. It is desirable to avoid treatment with hydrochloric acid for regulatory reasons (possible production of chloro-propanol derivatives), but hydrolysis with for example acetic acid may be desirable.
In the following descriptions the term xe2x80x9cCentratexe2x80x9d is used for the extracellular liquid recovered by the heat shock treatment of a suspension of Fusarium at about 70xc2x0 C. in the presence of its growth medium after separation of the cellular material. The term FDC means xe2x80x9cfreeze dried centratexe2x80x9d.